_drop_unique_constraint_in_sqlite() drops all unique constraints rather than given one

[Viktor Serhieiev]

steps to reproduce:

- create table with two unique constraints
- drop the first one

Expected result - table has one unique constraint.
Actual result - table has no unique constraints.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/30852

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/30852
Committed: http://github.com/openstack/nova/commit/251a4b8453a7a0218badd805d6f805a5c6d78a24
Submitter: Jenkins
Branch: master

commit 251a4b8453a7a0218badd805d6f805a5c6d78a24
Author: Victor Sergeyev <email address hidden>
Date: Wed May 29 11:54:10 2013 +0300

    Fix _drop_unique_constraint_in_sqlite() function.

    We got incorrect unique constrains in function
    _drop_unique_constraint_in_sqlite().
    New function `_get_unique_constraints_in_sqlite()` was added to fix it.

    Change-Id: Iebb4c0e6c3e6a069ba5cde2fdb2a2ff1200b826f
    Fixes: bug 1184526